From the Guidelines
Non-contrast CT is typically the preferred initial imaging modality for stroke workup, as it is highly sensitive for detecting acute hemorrhage, which is a critical distinction to make early in the workup as it significantly alters management 1. This is because the presence of hemorrhage is a contraindication for thrombolytic therapy, and non-contrast CT can quickly and accurately identify hemorrhage, allowing for rapid assessment and potential intervention. Additionally, non-contrast CT is quicker and more readily available than contrast CT, making it a practical choice for initial stroke evaluation 1.
The American Heart Association/American Stroke Association guidelines recommend that all patients with suspected acute stroke undergo immediate noncontrast brain CT imaging to guide hyperacute care 1. The Canadian Stroke Best Practice Recommendations also suggest that noncontrast brain CT imaging should be performed immediately in patients with suspected acute stroke, followed by vascular imaging with CT angiography to guide hyperacute care 1.
While contrast CT, including CT perfusion and CT angiography, can provide additional information about the state of the tissue and the location of a vascular clot, it is not typically used as the initial imaging modality for stroke workup 1. This is because contrast CT is not necessary for detecting acute hemorrhage, and it may delay treatment with thrombolytic therapy or endovascular therapy 1. However, advanced CT imaging, including CT perfusion and CT angiography, may be considered as part of the initial imaging protocol in patients with ischemic stroke who are clinically eligible for acute stroke treatments, as it can provide valuable information about the ischemic penumbra and guide treatment decisions 1.
Overall, the speed, availability, and sensitivity of non-contrast CT make it the initial imaging modality of choice for stroke evaluation, with contrast CT and advanced imaging modalities playing a secondary role in guiding treatment decisions 1.
From the Research
Imaging Modalities for Initial Stroke Workup
- Non-Contrast Computed Tomography (CT) is the most commonly used initial imaging tool to evaluate stroke, due to its exquisite sensitivity for hemorrhage, rapid acquisition, and widespread availability 2.
- The primary role of Non-Contrast CT is to exclude intracranial hemorrhage and directly visualize parenchymal changes of early infarct 3.
Comparison of Non-Contrast CT and Contrast CT
- Non-Contrast CT has limited sensitivity and moderate interobserver variability in detecting early infarcts 3.
- CT Angiography (CTA) is used primarily to identify intracranial large vessel occlusions and cervical carotid or vertebral artery disease, and is highly sensitive 2.
- CT Perfusion is widely used in endovascular therapy trials, but its use is not universally agreed upon, with some studies suggesting that Non-Contrast CT is comparable to CT Perfusion in selecting patients for endovascular treatment 4.
Predicting Final Infarct Size
- Non-Contrast CT has a stronger correlation with final infarct size than CT Angiography Source Images (CTASIs) 5.
- CTASIs can overestimate final infarct size, particularly in patients who undergo intravenous thrombolysis or mechanical thrombectomy 5.
- The Alberta Stroke Program Early CT Score (ASPECTS) on Non-Contrast CT is a reliable predictor of final infarct size and outcomes 5, 4.